Electric circuit breakers must subscribe to rigid industrial specifications and requirements to insure operation under extreme atmospheric conditions. To insure release of the circuit breaker operating mechanism during a tripping function, the circuit breaker latch and cradle assemblies are coated with a lubricating grease. Other circuit breaker components are coated with an insulative material to deter the transfer of circuit current other than through the circuit breaker contacts.
U.S. Pat. No. 3,953,812 teaches insulative material such as phosphate, silicon, varnish and the like to prevent the transfer of current between the circuit breaker cradle and armature.
U.S. Pat. No. 3,979,704 discloses that zinc phosphate and zinc chromate coatings should be applied to circuit breaker components when the circuit breaker is immersed in the liquid dielectric contained within a distribution transformer. The zinc phosphate and zinc chromate coatings protect the circuit breaker components from chemically reacting with the dielectric without interfering with the motility of the components.
When a circuit breaker employs a self-contained electronic trip unit, an actuator unit is required to interface between the circuit breaker operating mechanism and the trip unit in order to separate the circuit breaker contacts upon the occurrence of pretermined overcurrent conditions. U.S. Pat. No. 4,806,893, which Patent is incorported herein for purposes of reference, describes one such actuator unit.
U.S. Pat. Nos. 4,789,848 and 4,736,174 describe the latching and operating mechanisms used within the aforementioned U.S. Pat. No. 4,806,893 and are incorporated herein for purposes of reference. Both of these Patents should be reviewed for their description of the interaction between the motile circuit breaker components.
U.S. Pat. Nos. 4,733,211 and 4,782,583 describe the crossbar assembly that interfaces between the circuit breaker movable contact arm and the operating mechanism. Both of these Patents are also incorporated herein for reference purposes.
The components within the latching, operating mechanism and crossbar assemblies that slidingly interface with each other are each selectively coated to reduce the coefficient of friction inparted to these components by the loading provided by the powerful operating springs contained within the operating mechanism assembly and to protect the components from reacting with the environment. When such components are previously coated with zinc or tin compounds in accordance with the prior art, the zinc or tin material must first be selectively removed from the areas of those components that are to be coated with a lubricating grease to maintain a low coefficient of friction and protect the areas from the environment. The coatings are removed to prevent the "galling" of the materials used to form the coatings, which occurs when the materials are subjected to the loading provided by the operating springs. The galling could substantially increase the coefficient of friction and interfere with the operation of the components. The selective removal of the zinc or tin coating is economically infeasible when such circuit breaker components are robotically assembled.
The moving components that form part of the actuator unit described in aforementioned U.S. Pat. No. 4,806,893 should also be coated to provide a low coefficient of friction and to prevent oxidation. Because of the small size of these components, the removal of the protective coating is also economically infeasible.
The present invention accordingly, describes compositions for coating selected circuit breaker components without requiring removal of the coating and substituting the coating with lubricating grease.